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[PATCH 1/2] cpuhotplug/nohz: Remove offline cpus from nohz-idle state

To: Russell King <linux@arm.linux.org.uk>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Stephen Boyd <sboyd@codeaurora.org>, linux-arm-kernel@lists.infradead.org, Mike Frysinger <vapier@gentoo.org>, uclinux-dist-devel@blackfin.uclinux.org, Ralf Baechle <ralf@linux-mips.org>, linux-mips@linux-mips.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, linuxppc-dev@lists.ozlabs.org, Martin Schwidefsky <schwidefsky@de.ibm.com>, linux-s390@vger.kernel.org, Paul Mundt <lethal@linux-sh.org>, linux-sh@vger.kernel.org, "David S. Miller" <davem@davemloft.net>, sparclinux@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, mhocko@suse.cz, srivatsa.bhat@linux.vnet.ibm.com
Subject: [PATCH 1/2] cpuhotplug/nohz: Remove offline cpus from nohz-idle state
From: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Date: Thu, 3 Jan 2013 18:58:38 -0800
Cc: linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Srivatsa Vaddagiri <vatsa@codeaurora.org>
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Modify idle loop of arm, mips, s390, sh and x86 architectures to exit from nohz
state before dying upon hot-remove. This change is needed to avoid userspace
tools like top command from seeing a rollback in total idle time over some
sampling periods.

Additionaly, modify idle loop on all architectures supporting cpu hotplug to
have idle thread of a dying cpu die immediately after scheduler returns control
to it. There is no point in wasting time via calls to *_enter()/*_exit() before
noticing the need to die and dying.

Additional ARM specific change:
        Revert commit ff081e05 ("ARM: 7457/1: smp: Fix suspicious
RCU originating from cpu_die()"), which added a RCU_NONIDLE() wrapper
around call to complete(). That wrapper is no longer needed as cpu_die() is
now called outside of a rcu_idle_enter()/exit() section. I also think that the
wait_for_completion() based wait in ARM's __cpu_die() can be replaced with a
busy-loop based one, as the wait there in general should be terminated within
few cycles.

Cc: Russell King <linux@arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: uclinux-dist-devel@blackfin.uclinux.org
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: linux-sh@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: mhocko@suse.cz
Cc: srivatsa.bhat@linux.vnet.ibm.com
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
---
 arch/arm/kernel/process.c      |    9 ++++-----
 arch/arm/kernel/smp.c          |    2 +-
 arch/blackfin/kernel/process.c |    8 ++++----
 arch/mips/kernel/process.c     |    6 +++---
 arch/powerpc/kernel/idle.c     |    2 +-
 arch/s390/kernel/process.c     |    4 ++--
 arch/sh/kernel/idle.c          |    5 ++---
 arch/sparc/kernel/process_64.c |    3 ++-
 arch/x86/kernel/process.c      |    5 ++---
 9 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index c6dec5f..254099b 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -191,11 +191,6 @@ void cpu_idle(void)
                rcu_idle_enter();
                ledtrig_cpu(CPU_LED_IDLE_START);
                while (!need_resched()) {
-#ifdef CONFIG_HOTPLUG_CPU
-                       if (cpu_is_offline(smp_processor_id()))
-                               cpu_die();
-#endif
-
                        /*
                         * We need to disable interrupts here
                         * to ensure we don't miss a wakeup call.
@@ -224,6 +219,10 @@ void cpu_idle(void)
                rcu_idle_exit();
                tick_nohz_idle_exit();
                schedule_preempt_disabled();
+#ifdef CONFIG_HOTPLUG_CPU
+               if (cpu_is_offline(smp_processor_id()))
+                       cpu_die();
+#endif
        }
 }
 
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 84f4cbf..a8e3b8a 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -251,7 +251,7 @@ void __ref cpu_die(void)
        mb();
 
        /* Tell __cpu_die() that this CPU is now safe to dispose of */
-       RCU_NONIDLE(complete(&cpu_died));
+       complete(&cpu_died);
 
        /*
         * actual CPU shutdown procedure is at least platform (if not
diff --git a/arch/blackfin/kernel/process.c b/arch/blackfin/kernel/process.c
index 3e16ad9..2bee1af 100644
--- a/arch/blackfin/kernel/process.c
+++ b/arch/blackfin/kernel/process.c
@@ -83,10 +83,6 @@ void cpu_idle(void)
        while (1) {
                void (*idle)(void) = pm_idle;
 
-#ifdef CONFIG_HOTPLUG_CPU
-               if (cpu_is_offline(smp_processor_id()))
-                       cpu_die();
-#endif
                if (!idle)
                        idle = default_idle;
                tick_nohz_idle_enter();
@@ -98,6 +94,10 @@ void cpu_idle(void)
                preempt_enable_no_resched();
                schedule();
                preempt_disable();
+#ifdef CONFIG_HOTPLUG_CPU
+               if (cpu_is_offline(smp_processor_id()))
+                       cpu_die();
+#endif
        }
 }
 
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index a11c6f9..41102a0 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -71,13 +71,13 @@ void __noreturn cpu_idle(void)
                                start_critical_timings();
                        }
                }
+               rcu_idle_exit();
+               tick_nohz_idle_exit();
+               schedule_preempt_disabled();
 #ifdef CONFIG_HOTPLUG_CPU
                if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map))
                        play_dead();
 #endif
-               rcu_idle_exit();
-               tick_nohz_idle_exit();
-               schedule_preempt_disabled();
        }
 }
 
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index ea78761..39ad029 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -102,11 +102,11 @@ void cpu_idle(void)
                ppc64_runlatch_on();
                rcu_idle_exit();
                tick_nohz_idle_exit();
+               schedule_preempt_disabled();
                if (cpu_should_die()) {
                        sched_preempt_enable_no_resched();
                        cpu_die();
                }
-               schedule_preempt_disabled();
        }
 }
 
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 536d645..5290556 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -66,8 +66,6 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
  */
 static void default_idle(void)
 {
-       if (cpu_is_offline(smp_processor_id()))
-               cpu_die();
        local_irq_disable();
        if (need_resched()) {
                local_irq_enable();
@@ -95,6 +93,8 @@ void cpu_idle(void)
                if (test_thread_flag(TIF_MCCK_PENDING))
                        s390_handle_mcck();
                schedule_preempt_disabled();
+               if (cpu_is_offline(smp_processor_id()))
+                       cpu_die();
        }
 }
 
diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c
index 0c91016..f8bc2f0 100644
--- a/arch/sh/kernel/idle.c
+++ b/arch/sh/kernel/idle.c
@@ -96,9 +96,6 @@ void cpu_idle(void)
                        check_pgt_cache();
                        rmb();
 
-                       if (cpu_is_offline(cpu))
-                               play_dead();
-
                        local_irq_disable();
                        /* Don't trace irqs off for idle */
                        stop_critical_timings();
@@ -115,6 +112,8 @@ void cpu_idle(void)
                rcu_idle_exit();
                tick_nohz_idle_exit();
                schedule_preempt_disabled();
+               if (cpu_is_offline(cpu))
+                       play_dead();
        }
 }
 
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index cdb80b2..01589e7 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -105,13 +105,14 @@ void cpu_idle(void)
                rcu_idle_exit();
                tick_nohz_idle_exit();
 
+               schedule_preempt_disabled();
+
 #ifdef CONFIG_HOTPLUG_CPU
                if (cpu_is_offline(cpu)) {
                        sched_preempt_enable_no_resched();
                        cpu_play_dead();
                }
 #endif
-               schedule_preempt_disabled();
        }
 }
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 2ed787f..3d5f142 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -331,9 +331,6 @@ void cpu_idle(void)
                while (!need_resched()) {
                        rmb();
 
-                       if (cpu_is_offline(smp_processor_id()))
-                               play_dead();
-
                        /*
                         * Idle routines should keep interrupts disabled
                         * from here on, until they go to idle.
@@ -366,6 +363,8 @@ void cpu_idle(void)
                preempt_enable_no_resched();
                schedule();
                preempt_disable();
+               if (cpu_is_offline(smp_processor_id()))
+                       play_dead();
        }
 }
 
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